Phased array antennas include a plurality of antenna elements spaced apart from each other by known distances coupled through a plurality of phase shifter circuits to either or both of a transmitter or receiver. There is a desire to lower acquisition and life cycle costs of radio frequency (RF) systems that utilize phased array antennas (or more simply “phased arrays”). One way to reduce costs when fabricating RF systems is to utilize printed wiring boards (PWBs) (also sometimes referred to as printed circuit boards or PCBs), which allow use of more effective manufacturing techniques.
As is known, phased array antenna systems are adapted to produce a beam of radio frequency energy (RE) and direct such beam along a selected direction by controlling the phase (via the phase shifter circuitry) of the RF energy passing between the transmitter or receiver and the array of antenna elements. In an electronically scanned phased array, the phase of the phase shifter circuits (and thus the beam direction) is selected by sending a control signal or word to each of the phase shifter sections. The control word is typically a digital signal representative of a desired phase shift, as well as a desired attenuation level and other control data.
Phased array antennas are often used in both defense and commercial electronic systems. For example, Active Electronically Scanned Arrays (AESAs) are in demand for a wide range of defense and commercial electronic systems such as radar surveillance, terrestrial and satellite communications, mobile telephony, navigation, identification, and electronic counter measures. Such systems are often used in radar for land base, ship and airborne radar systems and satellite communications systems. Thus, the systems are often deployed on a single structure such as a ship, aircraft, missile system, missile platform, satellite, or building where a limited amount of space is available.
AESAs offer numerous performance benefits over passive scanned arrays as well as mechanically steered apertures. However, the costs associated with deploying AESAs can limit their use to specialized military systems. An order of magnitude reduction in array cost could enable widespread AESA insertion into military and commercial systems for radar, communication, and electronic warfare (EW) applications. The performance and reliability benefits of AESA architectures could extend to a variety of platforms, including ships, aircraft, satellites, missiles, and submarines. Reducing fabrication costs and increasing the quantity of components being manufactured can drive down the costs of the components and thus the cost of the AESAs.
With the desire to reduce cost of antennas, and in particular the cost of antennas having relatively large apertures, it has become common to develop the antenna aperture as an array of active aperture sub-arrays. These sub-arrays typically have their own internal RF power dividers, driver amplifiers, time delay units, logic distribution networks, DC power distribution networks, DC/DC converters, and accessible ports for RF, logic, DC power, and thermal management interfaces. It would desirable if each of the sub-arrays could be manufactured the same and be used interchangeably in the fabrication of the complete array. But when the aperture is formed from sub-arrays, it has, heretofore, lacked flexibility because the RF distribution networks required for receive beam formation and exciter output distribution are hardwired into the aperture backplane and position dependent in detail. Thus, typical AESA apertures are not configured such that the sub-arrays are interchangeable.
To further complicate the problem, a tracking radar employing a highly directive antenna pattern (narrow main beam) seeks to keep the antenna electrical boresight aligned with a target of interest. The method typically used to track targets is monopulse beamforming where the angular location of a target is obtained by comparison of signals received simultaneously in two antenna patterns (called the “elevation monopulse pattern” and “azimuth monopulse pattern”).
Presently, there are two basic approaches for AESA monopulse beamforming, analog beamforming, and combined analog-digital beamforming. In analog beamforming, an analog RF feed network combines each AESA Transmit/Receive (T/R) channel into sub-arrays; each sub-array has a unique RF feed network that is designed to couple and weight T/R channel RF receive signals to produce an array-level monopulse pattern in elevation and azimuth angle.
In combined analog-digital beamforming, an analog RF feed network combines each AESA T/R channel into sub-arrays where each unique RF feed network is designed to couple and weight T/R channel RF receive signals. Analog to Digital (A/D) converters at each sub-array produce digital signals that are then combined to form the final array level monopulse pattern in elevation and azimuth angle.
Thus, elevation and azimuth monopulse patterns can be generated with analog beamforming techniques, digital beamforming techniques, or a combination of both analog and digital beamforming.
What is needed is an AESA phased array architecture that enables the use of a beamforming RF feed network that is identical for each sub-array, provides the basic monopulse function, and reduces non-recurring engineering (NRE) cost.